Heme oxygenase-1 (HO-1) catalyzes the first step in the degradation of heme. HO-1 cleaves the α-meso carbon bridge of b-type heme molecules by oxidation to yield equimolar quantities of biliverdin IXa, carbon monoxide (CO), and free iron. Subsequently, biliverdin is converted to bilirubin via biliverdin reductase, and the release of Fe2+ from heme induces the expression of the Fe2+ sequestering protein ferritin, which acts as an anti-oxidant by limiting the ability of Fe2+ to participate in the generation of free radicals through the Fenton reaction.